1. Field of the Invention
The present invention refers to a vascular access device, in particular for purification treatments of the blood.
2. Prior Art
There are many patients who must submit periodically and with a certain frequency to blood purification treatments such as dialysis. For these patients, in order to eliminate the repeated insertion of needles for taking the blood to be purified and the inlet of the purified blood, there have been developed recently the so-called `vascular access` devices which are inserted permanently in the body of the patient and connected to his blood vessels.
Of this art a certain number of vascular access devices are known which comprise essentially a hollow body with apertures communicating with a duct integral therewith, which is grafted onto a blood vessel (artery or vein). Inside the hollow body there is housed a valve with passages which in one of its positions establishes communication between the blood vessel and external ducts connecting with means for removal and admission of the blood. By turning the valve said communication is interrupted. Examples of such devices are described in the patents FR 2571260, U.S. No. 4108174, U.S. No. 4015601, U.S. No. 4108173.
In some cases it was preferred to avoid removal and admission of the blood in the same zone and a vascular access device was achieved having two separate ducts inserted in different blood vessels (an artery and a vein) first connected through a fistule or bypass produced artificially. Said device is described in patents U.S. No. 4092983 and U.S. No. 4108174.
The drawback common to all the devices of the known art lies in the fact that not all the blood arriving in the vessel is routed to the purification equipment. A non-negligible part goes beyond the removal zone and mixes with the blood already purified. In addition, part of the returning blood can be recirculated by immediate intake back into the dialysis apparatus. As a result the efficiency of the purification treatment is reduced.
At the same time the formation of artificial fistules always calls for a surgical operation which it is not always possible to perform.
Another considerable drawback of said devices consists of the possible formation of coagulated blood and thrombi in the graft zone which must be removed quickly to avoid occlusion of the grafted duct.
Lastly, the need for periodic cleaning and maintenance of the device without removing said device from the body must be met.